An organic solvent, a binder resin, and a pigment are combined and milled for use in the charge generation layer in the fabrication of organic photoreceptors. The pigment and binder resin are chosen to optimize their photoelectric properties, but it is not always possible to optimize the dispersion quality of the resulting coating solution. Charge generating solutions that become unstable over time are a common problem in the fabrication of certain organic photoreceptors. Unstable dispersions result in coating defects in the charge generating layer that lower coating yield during the fabrication process. There is a need, which the present invention addresses, for a manufacturing system that can continuously monitor the dispersion quality of the charge generating solution to be able to prevent coating defects by replacing the charge generating solution on the onset of loss of dispersion quality.
One device that may be effectively used as a tool to monitor dispersion quality is a Hele Shaw flow cell. A Hele Shaw flow cell comprises a pair of flat plates narrowly separated from each other by a fixed distance, and held parallel to each other, thereby creating a gap region between the two plates. The Hele Shaw cell is typically dimensioned such that the separation distance between the plates is several orders of magnitude less than the remaining two orthogonal dimensions defined by the planar surface of either of the plates. A further description of the Hele Shaw flow cell may be found in An Introduction to Fluid Dynamics by G. K. Batchelor (Cambridge University Press, 1967)(copies of the title page, pages 222-223 and 604-605 are attached).
At times over the past several years, a number of the co-inventors checked the quality of a charge generating dispersion batch by taking a small sample from the batch to a laboratory located away from the photoreceptor fabrication line, and running the sample through a rectangular Hele Shaw flow cell where a human operator using a microscope viewed the sample flowing through the flow cell. The batch was approved or disapproved for use in Xerox commercial photoreceptors based on the dispersion quality results of the sample. The sample was then typically discarded. A problem with the above described procedure is that manually checking a sample at a laboratory separated from the photoreceptor fabrication line is very inefficient from a manufacturing viewpoint. The present invention addresses this problem.
A flow cytometer for investigating particle constituents in liquids is described in Kosaka et al., U.S. Pat. No. 5,521,699.